Index: xmlrpc.php
===================================================================
RCS file: /cvs/drupal/drupal/xmlrpc.php,v
retrieving revision 1.19
diff -u -p -r1.19 xmlrpc.php
--- xmlrpc.php	13 Dec 2009 13:06:45 -0000	1.19
+++ xmlrpc.php	13 Aug 2010 13:14:00 -0000
@@ -16,6 +16,4 @@ drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
 include_once DRUPAL_ROOT . '/includes/xmlrpc.inc';
 include_once DRUPAL_ROOT . '/includes/xmlrpcs.inc';
 
-$services = module_invoke_all('xmlrpc');
-drupal_alter('xmlrpc', $services);
-xmlrpc_server($services);
+xmlrpc_server(module_invoke_all('xmlrpc'));
Index: includes/xmlrpcs.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/xmlrpcs.inc,v
retrieving revision 1.41
diff -u -p -r1.41 xmlrpcs.inc
--- includes/xmlrpcs.inc	31 Jul 2010 04:17:34 -0000	1.41
+++ includes/xmlrpcs.inc	13 Aug 2010 13:14:46 -0000
@@ -45,7 +45,9 @@ function xmlrpc_server($callbacks) {
   // We build an array of all method names by combining the built-ins
   // with those defined by modules implementing the _xmlrpc hook.
   // Built-in methods are overridable.
-  foreach (array_merge($defaults, (array) $callbacks) as $key => $callback) {
+  $callbacks = array_merge($defaults, (array) $callbacks);
+  drupal_alter('xmlrpc', $callbacks);
+  foreach ($callbacks as $key => $callback) {
     // we could check for is_array($callback)
     if (is_int($key)) {
       $method = $callback[0];
Index: modules/system/system.api.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.api.php,v
retrieving revision 1.184
diff -u -p -r1.184 system.api.php
--- modules/system/system.api.php	8 Aug 2010 19:45:37 -0000	1.184
+++ modules/system/system.api.php	13 Aug 2010 13:24:27 -0000
@@ -1846,37 +1846,33 @@ function hook_xmlrpc() {
 }
 
 /**
- * Alter the definition of XML-RPC methods before they are called.
+ * Alters the definition of XML-RPC methods before they are called.
  *
- * This hook lets at module modify the callback definition for already
- * declared XML-RPC methods, when they are being invoked by a client.
+ * This hook allows modules to modify the callback definition of declared
+ * XML-RPC methods, right before they are invoked by a client. Methods may be
+ * added, or existing methods may be altered.
  *
- * This hook is invoked by xmlrpc.php. The method definitions are
- * passed in by reference. Each element of the $methods array is one
- * callback definition returned by a module from hook_xmlrpc. Additional
- * methods may be added, or existing items altered.
- *
- * Modules implementing this hook must take care of the fact that
- * hook_xmlrpc allows two distinct and incompatible formats for callback
- * definition, so module must be prepared to handle either format for
- * each callback being altered.
+ * Note that hook_xmlrpc() supports two distinct and incompatible formats to
+ * define a callback, so care must be taken when altering other methods.
  *
  * @param $methods
- *   Associative array of method callback definitions returned from
- *   hook_xmlrpc.
+ *   An asssociative array of method callback definitions, as returned from
+ *   hook_xmlrpc() implementations.
  *
  * @see hook_xmlrpc()
+ * @see xmlrpc_server()
  */
 function hook_xmlrpc_alter(&$methods) {
-
-  // Direct update for methods defined the simple way
+  // Directly change a simple method.
   $methods['drupal.login'] = 'mymodule_login';
 
-  // Lookup update for methods defined the complex way
+  // Alter complex definitions.
   foreach ($methods as $key => &$method) {
+    // Skip simple method definitions.
     if (!is_int($key)) {
       continue;
     }
+    // Perform the wanted manipulation.
     if ($method[0] == 'drupal.site.ping') {
       $method[1] = 'mymodule_directory_ping';
     }